(1) Field of the Invention
This invention relates to an improved vacuum cleaning apparatus which includes at least one cyclone unit for dust extraction. Preferably the present invention relates to a vacuum cleaning apparatus of the type in which a cleaner duct or pipe for contacting a dirty surface is connected to the interior of a casing in which an air-flow is set up by a motor-driven fan. The casing contains at least one cyclone unit operating to extract dirt particles (dust and other extraneous or foreign matter) from the air-flow therethrough, and to deposit the extracted dirt.
(2) Prior Art
A cleaning apparatus based only on cyclone units has the advantage that dust bags are not required as dirt can be discharged from the apparatus by removing and separating the cyclone from the surrounding casing. Other advantages are that the air discharged from the appliance is substantially dust free and the use of filters as main cleaning elements is avoided. Conventionally the body of a prior art cyclone unit is substantially frusto-conical with the narrower end lower most. This cyclone works very well, however, improvements in efficiency were needed.
EPC Patent Specification No. 0 042 723 and U.S. Patent application Ser. No. 452,917, abandoned, continuing application Ser. No. 640,758, now U.S. Pat. No. 4,593,429 describe an outer cyclone or casing of lower efficiency having a cylindrical form. The lower efficiency is in respect of the cyclone's capability of extracting very fine dust particles. A higher efficiency inner cyclone of frusto-conical shape is provided inside the outer cyclone. In these cyclones dirty air is caused to enter the cyclone tangentially at the upper end of the cyclone body, cleaned air is exhausted from the cyclone body through an axially located exhaust port in the upper half of the body and dust and other foreign particles collect at the bottom of the cyclone body. For dual cyclone apparatus the air flow is repeated in the same manner.
In both types of cyclone, i.e. the high efficiency frusto-conical and the low efficiency fine dust cyclone, particles collected at the bottom of the cyclone may become re-entrained in the air-flow in the body, or may never settle out at the bottom of the body, remaining entrained in the air-flow through the cyclone. In either of these circumstances the dust particles are caused to rise up towards the exhaust port, in the axially upwardly moving air-flow within the cyclone body from the dust collected in the cyclones. Thus said dust is exhausted from the cyclone contaminating the otherwise cleaned air.